1. Field
The presently disclosed subject matter relates to an LED lighting apparatus for a vehicle lamp, and more particular to an LED vehicle lighting apparatus including a user friendly fail safe circuit in which an amount of forward voltage for LEDs connected in series is larger than a supply voltage of a battery.
2. Description of the Related Art
Various LEDs have been used as a light source for vehicle lamps (e.g., headlights, tail-lights, stop lights, signal lights, etc.) such as in autos, trucks, buses and so on. One reason is that LEDs can emit variously-colored lights so as to match those typically used in vehicle lamps while the structure therefore can be thin and small in size. In addition, LEDs may be great for ecology due to a long life, etc.
When LEDs are used as a light source for the vehicle lamps, a plurality of LEDs may be connected in series in order to conform to a light distribution standard for a vehicle lamp. For example, a lighting circuit for a vehicle lamp including a plurality of LEDs is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2006-103404). FIG. 5 is a circuit diagram showing the conventional lighting circuit for a vehicle lamp that is disclosed in Patent Document No. 1.
The lighting circuit can control the plurality of LEDs LB to create a low beam for a headlight, and can control the plurality of LEDs HB to create a high beam for a headlight. In these LEDs LB and HB, around 10 pieces of LEDs to 20 pieces of LEDs can be operated to emit light with a brightness suitable for a vehicle headlight. When these LEDs are connected in parallel, the interconnection may be subject to certain complications, and therefore these LEDs are usually connected in series. Thus, the amount of forward voltage for the LEDs may become approximately 35 volts to 70 volts when the LEDs are composed of white LEDs based upon a blue LED and a yellow phosphor.
However, although a supply voltage of a vehicular battery may change from about 10 volts to 16 volts according to a discharge/charge status of a vehicular battery, these LED cannot typically be driven directly by the vehicular battery because of the low voltage. Therefore, the conventional lighting circuit provides these LEDs LB and HB with a boosted voltage by providing a DC-DC converter between the vehicular battery and these LEDs LB and HB.
The lighting circuit includes: a transformer 2a having a primary coil and a secondary coil, and one terminal of the primary coil connected to a battery 1 via a switch SW; a switching element Qp having a drain that is connected to the other terminal of the primary coil of the transformer 2a; a diode 2c having an anode that is connected to one terminal of the secondary coil of the transformer 2a; a capacitor 2d connected between a cathode of the diode 2c and the other terminal of the secondary coil of the transformer 2a; a resistor Rs located between a cathode of a last LED of the LEDs HB and the other terminal of the secondary coil of the transformer 2a that is connected to ground; and a controller 2b having a feedback terminal and an output that is connected to a gate of the switching element Qp.
The switching element Qp is alternated on and off in accordance with a pulse width modulation (PWM) signal output from the controller 2b, which is configured to control the on and off time of the switching element Qp under a feed back control so that a current If flowing in the resistor Rs for detecting the current of the LEDs can be constant, if a voltage of the battery 1 and a load of these LEDs LB and HB change.
The switching element Qp can be alternately turned on and off at a frequency ranging between ten thousand Hertz to several hundred thousand Hertz, and therefore a DC voltage of the battery 1 can be converted into an AC voltage. The AC voltage may be changed to a smooth DC voltage with the diode 2c and the capacitor 2d, and the LEDs LB and HB can emit light by providing them with this boosted DC voltage.
In the above-described lighting circuit, when a driver turns on a high beam for a headlight, these LEDs LB and HB can emit light in high beam mode by turning on the switch SW. When the driver turns on a low beam for the headlight, a voltage between the LEDs HB becomes a low voltage that is close to zero voltage by turning on a switching element Qs with a signal S, the LEDs LB can emit light as the low beam while the LEDs HB for the high beam turn off.
According to the conventional lighting circuit described above, when a disconnection is caused in a circuit between the LEDs HB at the high beam, the lighting circuit includes a characteristic or problem in that both the LEDs LB and HB cannot work simultaneously. Therefore, when detecting a disconnection between the LEDs HB, the LEDs LB can light as a fail-safe function for the high beam of the headlight by turning on the switching element Qs.
An LED lighting apparatus including a number of LEDs is disclosed in Patent Document No. 2 (U.S. Patent Application Publication No. 2007/0273306). The conventional LED lighting apparatus can drive the many LEDs connected in series using a boosting circuit and an inverted boosting circuit based on a controller. The LED lighting apparatus includes a shutdown circuit to stop supply from a power supply when a load that includes the LEDs is in a circuit that is either opened or shorted as a fail-safe function.
The above-referenced Patent Documents are listed below and are hereby incorporated with any related English abstracts in their entireties.
1. Patent Document No. 1: Japanese Patent Application Laid Open JP2006-103404
2. Patent Document No. 2: U.S. Patent Application Publication No. 2007/0273306 to Fujino et al. published on Nov. 29, 2007
In the conventional lighting circuit shown in FIG. 5, because the controller 2b may be generally composed of an expensive and specific IC and peripheral parts, the LEDs LB and HB may be controlled by the one controller 2b. Therefore, when the controller 2b has a breakdown due to a various causes, such as a surge and the like, the conventional light unit including both LEDs LB and HB may not light.
According to the conventional lighting apparatus that is disclosed in Patent Document No. 2, the controller may not breakdown because of the shutdown circuit even if an over current flows in the circuit or in the LEDs occurs in the circuit. However, the LEDs may not light, and may need to be replaced with new LEDs before operation can begin again. Therefore, the fail safe function may not be sufficient when the lighting apparatus is used for a vehicle lamp.
The disclosed subject matter has been devised to consider the above and other problems and characteristics. Thus, an embodiment of the disclosed subject matter can include an LED vehicle lighting apparatus having a user friendly fail safe function for supplying LEDs connected in series with a requisite voltage and power even if the amount of forward voltage of LEDs connected in series is larger than a supply voltage of a battery. The various characteristics, features, and problems described above are thus addressed and possibly reduced or changed while also addressing and possibly reducing other associated problems regardless of the above-described combined headlight.